MBS is primarily to let you store and access your data in datastore, directly from devices, without necessarily having your own server process.
For a streaming service, you will need to have a server process. Best way is to store files with full control, is to use BlobStore and use the BlobReader to read and serve in chunks.
More convenient way, but with less control is to store in cloud-storage and serve directly to client with cloud-storage URI, without streaming through your server, in which case, you do not need a server process.